Mobile communication devices have become increasingly common in current society for providing wireless communication services. The prevalence of these mobile communication devices is driven in part by the many functions that are now enabled on such devices. Increased processing capabilities in such devices means that mobile communication devices have evolved from being pure communication tools into sophisticated mobile multimedia centers that enable enhanced user experiences.
A mobile communication device may be configured to support carrier aggregation, in which the mobile communication device simultaneously communicates (transmits and/or receives) a pair of radio frequency (RF) signals in a pair of different frequency bands. For example, the mobile communication device can be configured to communicate one RF signal in a selected frequency band (e.g., long-term evolution (LTE) band 41), while simultaneously communicating second RF signal in one of other frequency bands (e.g., LTE band 1, 25, 30, 40, or 66).
In one possible configuration, the mobile communication device may include a filter circuit specifically for LTE band 41 and a multi-band filter circuit(s) for the other LTE bands. Accordingly, the mobile communication device can be dynamically configured to support carrier aggregation between LTE band 41 and any of the other LTE bands. In this regard, to help mitigate interferences between LTE band 41 and the other LTE bands, the LTE band 41 filter circuit needs to present higher and less lossy impedance to each of the other LTE bands located outside LTE band 41. Hereinafter, impedance presented by a filter circuit of a selected frequency band against any other frequency band outside the selected frequency band is referred to as “out-of-band” impedance.
Notably, the LTE band 41 filter circuit may need to present different out-of-band impedance for each of the other LTE bands. In a conventional approach, the LTE band 41 filter circuit may be coupled to an adjustable capacitor(s), which can be adjusted to influence the out-of-band impedance presented by the LTE band 41 filter circuit. However, such a conventional approach may be ineffective in providing the out-of-band impedances at the higher and less lossy level to enable sufficient interference mitigation during carrier aggregation, particularly when a pair of frequency bands involved in the carrier aggregation operation is close to each other.